Work on the relations of children's emotional experience or emotion regulation to social and mental health outcomes is limited, especially research that is optimally suited for the evaluation of causal relations. A 6-year follow-up of a sample of typical school children moving into early adolescence, 2- and 4-year follow-ups of a sample including at risk elementary school children, and a short-term longitudinal study of young children are proposed. A multimethod approach, using self-reports, observations, and behavioral measures, as well as facial and physiological markers of emotion, in a combination of naturalistic and laboratory studies, will be used. The goals are to examine the additive and interactive contributions of individual differences in dispositional regulation and negative emotionality to socio-emotional functioning and related behaviors, including socially appropriate behavior, positive peer relationships, and ego resiliency; externalizing and internalizing problem behaviors; the occurrence and valence of emotions in actual social interactions with parents or peers; and quality of actual coping behavior. We predict that emotionality often will influence the relation of regulation to outcomes; that low emotional (attentional) regulation, low resiliency, and overcontrol will be important in prediction of internalizing behaviors; that the relation of behavioral control to resiliency and internalizing problems will be nonlinear; and that different negative emotions will be differentially related to different kinds of problem behaviors. With multiple longitudinal assessments, one can assess if emotionality and regulation interaction in predicting outcomes when controlling for prior levels of these variables to examine whether across time prediction is mediated over time through regulation/emotionality, the outcome variable(s), or both. Developmental changes in childhood/adolescence in relations of emotionality, regulation, and resiliency to children's social functioning will be assessed. Another goal is to obtain data on the relations of children's emotionality, regulation, and social functioning to parental expression of emotion and emotion-relevant behavior, especially in stressful contexts. Analytic procedures will include structural equation and growth curve modeling. The findings will provide valuable information on the role of emotion, its regulation, and socialization, in children's social competence and adjustment in childhood and adolescence.